When an exporttree=yes remote has had a tree exported to it, but eg with
`git-annex export master --to foo --fast`, so not all the files have been
sent to it yet, `git-annex sync -Cfoo` will also export files in other
directories to it.

This seems like a bug, it ought to only export any files in the specified
directory.

Another way this can happen is `git-annex sync -Cfoo`, when file bar
has changed. Currently this exports bar to the export remote, but does
not send it to any other remotes, since it's not in directory foo.

Also this affects `git-annex satisfy`, and other related commands too.
--[[Joey]]

> Decided to just document this behavior since there does not seem to be
> any good alternative behavior. [[done]] --[[Joey]]
